I would like to know from forum experiences what has been the behaviour of internal bellows expansion joints installed on FCC VVS risers. Reporting of problems related with cracking of inconel bellows as well as coking and loss of bellows flexibility. Please share Luis Marques

Installation of double bellow system with red alarm .

Luis Bellows : single or double ply with two fixed ends are known to give cracking and failure problems - whether internal or external bellow usage in equipment meant to take uneven expansion, thermal stresses and also from corrosion-erosion problem in bellows. Multiple thin ply instead of single or double ply - different designs have been developed - Omega, V, U type designs are available with leading bellow manufacturers. Multiple thin ply designs are available from 1970 in the market which are more flexible and can take more distortion effect. Multiple thin ply construction bellows can take uneven stresses better even for fixed two ends comparatively easily than single or double ply bellow construction. Stress factor in multiple thin ply will be nearly 1/4th (one quarter or less) than that of single or double ply. If you can reduce stresses, cracking problem at ends due to uneven expansion or thermal stresses may not come. Coke particle entrainment will have to be attended. Although not related to FCC reactor internal bellow design, we have used successfully multiple thin ply - Omega design of Inconel 600 construction. We used quite successfully for several years- > 10-12 years i remember - in superheated steam carry over with possibilities of caustic or chlorides concentration (from steam at temperature 350-400 deg centigrade) from carry over suspended particlesalong with gas or liquid from CO2 absorber. This problem existed with bellows in a Methanator exchanger. As you may know, Inconel 600 will also crack at 350 or 450 deg cent due to both caustic or chloride concentration at the bellows but multiple thin ply design proved to be big success factor to reduce stresses below threshold values even with likely concentration of caustic or chlorides at that temperature. I believe that there could be designs available today with leading bellow design manufacturers - with multiple thin and also with an internal shield plate . Internal shield plate will only act as a barrier for any coke particle carry over which will get entrapped at the bellow grooves of any design (whether Omega, V or U design) Internal shield plate will prevent carry over of coke particles and may enable to prevent the problem of coking at the bellows i.e.,at the corrugated portions of Omega or V or U designs (all of multiple thin design) will not have direct coke particle carry over and coking. Internal shield plate may crack due to uneven expansion stresses at the fillet or stitch welded areas. This repair is comparatively easier than replacing an internal bellow with cracks. Trust this will help you to contact leading bellow manufacturers who make to ASME Code practices bellows of suitable design. C.V.Srinivasan Nishi Engineers Pvt Ltd India July 29, 2007 E-mail: nishi@vsnl.com >Thank you > >Krish123 & debasismitra > >Double ply bellows with leak indication, from my knowledge >are only used, in flue gas lines or stand pipes. > >Expansion joints bellows installed inside equipments such as >FCC Third Stage or FCC Reactor Riser are of one ply bellows >2 or 3 mm thick. > >At the moment we intend to revamp our FCC reactor for a VSS. >My concern is about the criticality of internal expansion >joint installed at the outlet duct of riser chamber. > >I would like to know from forum what is the behaviour of >this expansion joint. From my point of view even with steam >buffering I am expecting grew of coke build up in bellows >plies loss of bellows flexibility and deformation of chamber >riser dome bellow the expasion joint. > >Please share your experiences about this subject. > >Regards > >Luis Marques